In the first paper, “What is Epilepsy,” Kohrman introduces the topic for nonclinicians with an interest in epilepsy research. The second group of papers on “Where Do Seizures Occur,” describe the physiologic, clinical, and engineering aspects of localizing neuronal activity in the brain. The ultimate goal in this area of research is to identify the epileptic focus reliably by solving the so-called “inverse problem”, i.e., the reconstruction of activity within the brain from measurements on its surface or on the scalp. To that end, Tao et al. and Ebersole et al. present techniques useful in the clinical setting to interpret scalp recordings in terms of underlying cortical activity. The papers by Fuchs et al. and Ding et al. describe the development and evaluation of algorithms to compute and visualize activity within the brain's structure. Significant progress in this field has been made, and localization methods are proving to be a useful extension of EEG analysis. However, to increase the clinical value of localization methods, the limits of their resolving power must be further investigated and improved. Ultimately these techniques may provide an alternative to and reduce the need for intracranial recording, which remains the gold standard for the identification of the epileptic focus.
The third theme, “When Do Seizures Occur,” deals with the localization of seizure activity in time. The aim in this area of research is to detect, predict, or anticipate imminent seizures on the basis of features extracted from scalp or intracranial EEG recordings. Early work in this area optimistically reported the feasibility of this approach. The investigations of Lee et al. and Lehnertz et al. demonstrate that the current state-of-the-art is the early detection of seizure onset, when complete records from continuously monitored patient populations are evaluated. The use of long-term monitoring records, new evaluation tools, and a change of focus from single channel to multichannel recordings are required for further development in this area.
The contributions to the final theme, “Why (How) Do Seizures Occur,” focus on the mechanisms underlying epileptogenesis and seizure activity. Our poor understanding of these mechanisms is a principal reason for the limited success of anticonvulsant therapy, that being lack of seizure control in 1/3 of epilepsy patients. Papers by Trasande and Ramirez, Swiercz et al., and Li and Mogul describe recent progress in identifying the role of neuronal mechanisms and their control in experimental models of epilepsy. At the clinical level, signal processing applied to the analysis of EEG is an extensive area of epilepsy research describing the relationships between the activities of large neuronal populations. The paper by Towle et al. demonstrates this approach.